Automatic volume controls for radio receiving sets



June 11, 1935. R. M. PLANCK 2,004,294

AUTOMATIC VOLUME CONTROLS FOR RADIO RECEIVING SETS Filed Aug. 15, 1951 v' Q INVENTOR N T v Pu Mer/as 1 /0/76 BYZZW J m I I! W TORNEY' Patented June 11, 1935 o o i IT D STATE/S" PA Q E AUTOMATIC VOLUME ooN'rnorls FOR RAD) RECEIVING SETS, I i RusseH ll Iertes ilanok, JacksonfMich assignor,

' by inesneassignments, to Radio Corporation of America, NewYork, Y., a. corporation of I Delaware Application August 15, 1931, Serial No.1557,311

2 Claims. missu -20) This invention relates to radio receiving sets and more particularly .to automatic volume controls whereby volume may remain substantially uniform regardless of the strength of the signal reaching the antenna.

One object of the invention is to produce a volume control that is yautomaticin operation with minimum complication of circuit connec} Another object of the invention is to bias the amplifier tubes in a' radio set by a potential drop in the direct current circuit of the plate in the detector tube. I

Another object of the invention is, to construct a volume control in which the resistance used to furnish the dropforthe negative bias is also capable of hand manipulation to set the volume at any desired alue without changing circuit consisting of an inductance 3 and a variable capacity i althoughthe inductance may 1 be varied instead of the capacity, if desired. The

inductance and capacity are joined together in the grid 5 of thej first radio frequency tube T1. The opposite end of the capacity 4 is connected to ground 6 and the opposite end of the inductance 3 is connected through avariable tap I of v of the push-pull transformer in the plate cirresistance 8. l

The filament of the first radio frequency tube may be connected to a power supply but for simplicity in illustration Ihave generally indi-, cated the source at 9. One end of the filament is connected to point Iii which is joined to an intermediate portion of the power, supply re-,,

sistance I I which resistance has its negative end grounded at it. The, plate of radio frequency tube T1 is connected to the primary I3 and to a junction point I4 which is joined to the high,

potential end [5 of the resistance I I. The inductance 3 and the filament 9 are connected through small condensers I6, H, to the low potential end of the tuning condenser 4. The lower end of coil I3 is likewise connected tothe same point in the filament by a small condenser I8.

The radio frequency tubes T2, T3, or any greater or less number, are connected so that ductance.

their grids, I9, "20, are coupled to the preceding primaries I3 and H by secondaries 22 and 23., The tracing of the circuits in the second and third radio frequency stage will be, the same as has been described inconnection withthe first radiofrequency stage and a. detail description quency, tube T3 is coupled to the secondary 25 of the detector tube T4. Variable condenser 26 tuning purposes and the low potential end is grounded at 27. The filament of this detector tube is connected through a resistance, 28 and parallel condenser 29 to the ground'30. The plate of the detector: tube is connected through an inductance 3i having two condensers 32,33, connectedin series and in parallel of the in- The midpoint of the condensers is connected to theend of resistance 28, as shown, so as to furnish a radiofrequency bypass. The

plate circuit is then completed through the point in the power supply resistance II as shown. U

The primary 34, of the audio-transformer is coupled to :the secondary 35 of a push-pull amplifier. The method of connection-will be ob- I vious from the drawing and further description need not be made except tolstate that the loud speaker or other signal, receiving device (not shown) will be connected to the secondary 36 cuits of the tubes.

With the foregoing circuit arrangement direct current for the plate supply of the detector T4 will pass from the intermediate point 38 of the power supply resistance through volume control resistance 8 through the plate filament and resistance 28 to ground 30; and thence back to the low potential end of resistance II through ground I2. This will produce a potential drop in the resistance 8, depending upon the average amount of direct current flowing in that circuit.

The grids 5, I9 and 20 of theradio frequency 7 amplifier tubes being connected to the point I will have a negativebias because the filaments 10: is'connected in parallel with this secondary for r With bias detection increase of signal in the plate circuit of a detector increases the average direct current flow in the plate circuit. This increase of average direct current in the plate circuit of the detector increases the potential drop in resistance 8, thus increasing the drop between the points 38 and 39 that biases the amplifier tubes. This increase of bias on the amplifier tubes decreases the amplification of those tubes. Therefore when the signal tends to increase the circuit connection immediately tends to decrease the amplifying power of the tubes and weakens the signal. It of course takes an increase of signal to cause the volume control to function but this increase is kept to a minimum by the automatic control and thevolume is maintained reasonably constant regardless of strength of signal. In this respect the automatic volume control is comparable to the action of a fly ball governor on a steam engine. Having described my invention, what I claim 1. In a volume control for radio receiving sets, a direct current source of potential, a resistance connected to said source, a detector tube, a second resistance connected between a point on the first resistance and the output electrode of the detector, a third resistance connected between the cathode of the detector and a point in the first resistance negative to the first meritioned point, the grid of the detector being connected to a point in the third resistance negative to the first mentioned point, a radio frequency amplifier tube having its control electrode and cathode connected respectively to negative and positive points in the second resistance, and means to connect the output electrode of the radio frequency amplifier tube to the input electrode of the detector tube.

2. In a volume control for radio receiving sets, a direct current source of potential, a resistance connected to said source, a detector tube, a second resistance connected between an intermediate point on the first resistance and the output electrode of said detector, at third resistance connected between the cathode of the detector and the negative terminal of the first resistance, the grid of the detector being connected to said negative terminal, a radio frequency amplifier tube having its cathode connected to the junction point of the first and second resistances, and its control electrode connected to a point in the second resistance negative to said junction point, and means to connect the output electrode of the radio frequency tube with the input electrodeof the detector.

RUSSELL MERTES PLANCK. 

